1. Membrane properties of and cholesterol's interactions with a biologically relevant three-chain sphingomyelin: 3O-palmitoyl-N-palmitoyl-D -erythro-sphingomyelin
- Author
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Sergelius, Christian and Slotte, J. Peter
- Subjects
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CELL membranes , *CHOLESTEROL , *SOLUBILITY , *CALORIMETRY , *CYCLODEXTRINS , *PHOSPHOLIPIDS , *BILAYER lipid membranes - Abstract
Abstract: Sphingomyelins (SMs) are order-imposing phospholipids in cell membranes which interact favorably with cholesterol. The hydrophobic part of SM constitutes a long-chain base with an amide-linked acyl chain, whereas the polar head group is phosphocholine. The long-chain base has a free hydroxyl group in position 3, which is an important donor/acceptor in hydrogen bonding. In newborn mammals, a SM in which a palmitic acid is esterified to the 3-OH has been reported. We have synthesized this SM analog (3O-P-PSM) and studied its properties in bilayer membranes, and also determined its interactions with cholesterol. Fully hydrated 3O-P-PSM bilayers underwent a gel-to-liquid crystalline phase transition at 55.5°C (ΔH 8kcal/mol), which is about 15°C higher than the phase transition temperature of PSM. The 3O-P-PSM displayed rather poor miscibility with PSM in mixed bilayers, suggesting that the third acyl chain interfered significantly with lateral interactions. Bilayers made from 3O-P-PSM were much more resistant to detergent-induced solubilization than bilayers made from PSM. In binary bilayers, cholesterol was able to destabilize the gel phase, and order the fluid phase of 3O-P-PSM, in a concentration-dependent manner. Cholesterol was also able to form sterol-enriched ordered domains with 3O-P-PSM in fluid POPC bilayers. The interaction between cholesterol and 3O-P-PSM was not, however, as favorable as the interaction between cholesterol and PSM. It is unclear what physiological role 3O-P-PSM could play in newborn mammalian membranes. However, it is clear that 3O-P-PSM will form more highly ordered domains than PSM while still having a limited ability to interact with cholesterol. [Copyright &y& Elsevier]
- Published
- 2011
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